Implantable cardioverter defibrillators (ICDs) have traditionally been used in patients who survived, or have a high risk of experiencing, a sudden cardiac death event. More recently, indications have been expanded to include patients who have had asymptomatic nonsustained ventricular tachycardia, for example, with decreased ventricular function.
A typical ICD has one or more electrodes for delivering defibrillation shocks to a patient's heart. An ICD may use such electrodes, for example, upon detection of a ventricular tachycardia or a ventricular fibrillation. In general, after the ICD determines a need for a shock, a delay typically occurs wherein the ICD charges a shock capacitor. The ICD then discharges the capacitor to deliver a shock, typically of approximately 25 J. An ICD device may also repeat the charge and discharge cycle (e.g., for approximately 5 cycles). Other ICD devices may provide programmable low-energy cardioversion in addition to or in lieu of high-energy shocks. Yet other ICD devices provide a feature that is commonly referred to as “tiered therapy”, which typically includes antitachycardia pacing for painless (or relatively painless) termination of monomorphic ventricular tachycardias, programmable low-energy cardioversion, high-energy defibrillation, and backup bradycardia pacing.
To determine a need for a shock, an ICD typically has a lead placed in a patient's right ventricle where it provides for sensing of ventricular rate and/or other information for detection of abnormal cardiac behavior. Some ICD systems also include an atrial lead, which can, for example, be used to sense atrial information, to pace and/or to deliver other therapy. In general, an ICD having both atrial and ventricular leads is referred to as a dual-chamber ICD. Yet further, some ICDs and other implantable cardiac therapy devices have one or more electrodes capable of delivering an atrial shock. Hence, such devices may provide for atrial tiered therapy.
While various aforementioned ICDs or other devices may provide for more favorable outcomes, shock is often associated with patient pain and discomfort. A variety of approaches to alleviating and/or minimizing such pain and discomfort have been reported. One approach involves transcutaneous electrical nerve stimulation (TENS) for blocking transmission of sensory signals (e.g., sensory nerve blockade), another approach involves direct cerebral cortical stimulation, while yet another approach involves direct spinal cord stimulation (SCS). These approaches elicit such stimulation only after determination of a need for a shock and just prior to or in conjunction with delivery of the shock. Hence, for the any significant relief of shock-associated pain or discomfort, the analgesic effect of the stimulation should be nearly instantaneous.
For SCS, the reported analgesic effect is apparently immediate and due to inhibition of impulse transmission in small fiber afferents by activation of large fiber afferents on the associated spinal segmental level. However, other forms of nerve stimulation may have a time delay before production of any significant analgesia. Hence, methods that rely on delivery of analgesic stimulation just prior to or in conjunction with shock delivery may be suboptimal in reducing patient pain or discomfort.
Various exemplary methods, devices and/or systems presented herein aim to reduce or eliminate patient pain or discomfort via analgesic stimulation. In particular, several exemplary methods provide for analgesic stimulation in conjunction with levels of tiered therapy.